Steel strip and its manufacturing method

Abstract

A steel strip having excellent workability and corrosion resistance without the need for oil coating, and a method for manufacturing the same. The steel strip includes a substrate, and a phosphate layer and a stearic acid lubricant layer provided on the substrate. The upper surface of the steel strip includes a phosphate layer and a stearic acid lubricant layer, in that order from the inside to the outside, and has a surface roughness R in the range of 0.6 to 1.8 μm. a and R in the range of 6 to 16 μm z The lower surface of the strip has a stearic acid lubricant layer and a surface roughness R of 0.3 μm or less, which provides good surface lubrication during the rolling process. a and R of 2μm or less z It has good lubrication and high surface cleanliness. By using the steel strip designed with differentiated functionality of two surfaces according to the present invention, it can be directly stamped to process shell parts with high precision and large deformation, eliminating the traditional processes of coating, oiling, and post-forming cleaning required to manufacture shell parts with high precision and large deformation from traditional steel plates, and significantly improving the efficiency of part manufacturing. In addition, the steel strip has good rust and corrosion resistance, and its surface does not require oil coating treatment during storage and transportation.

Description

[Technical field]

[0001] The present invention relates to the field of metal material processing, and more particularly to a steel strip having excellent workability and corrosion resistance without the need for oil coating, and a method for producing the same. [Background technology]

[0002] In the field of metal material processing, continuous and efficient processing technology characterized by high precision, high complexity, and environmental protection requirements is widely used in the processing of automobile and machine parts. According to the extensive theoretical analysis of scientific experimental research and application implementation research, it is found that during the stamping process of shell parts with high precision and large deformation, the surface of the steel plate in contact with the female mold (mother mold) bears the main deformation friction force, and the surface of the steel plate in contact with the male mold (punch) bears a relatively small deformation friction force, mainly ensuring the dimensional accuracy of the inner surface. Therefore, the surface of the steel plate in contact with the female mold needs to provide sufficient lubrication during the deformation process. Rather, the surface of the steel plate in contact with the male mold does not need high lubrication performance, but needs extremely high surface cleanliness. In order to obtain shell parts with high dimensional accuracy / high surface quality, it is required that the two surfaces have different lubrication functions.

[0003] Material suppliers, such as JFE, Nippon Steel, and POSCO, mainly focus on developing products with excellent mechanical properties. In the field of research and development of stamping materials, the main focus is on double-sided coating treatment of steel strips (e.g., coating with a lubricating layer), as described in US Pat. No. 5,399,233, US Pat. No. 5,433,366, and US Pat. No. 5,433,233.

[0004] Regarding double-sided coating treatment of steel strip surface, the main process types include: (1) forming a micron or submicron organic coating on the surface of steel sheet by roll coating and bake hardening in a continuous manufacturing process, as described in U.S. Pat. No. 5,393,433, U.S. Pat. No. 5,493,637, and U.S. Pat. No. 5,523,363, and (2) forming a phosphating / passivation layer on the surface of steel sheet by spraying in a continuous manufacturing process, as described in U.S. Pat. No. 5,523,437.

[0005] Patent Document 5 discloses "Self-lubricating passivation solution and hot-dip galvanized self-lubricating steel sheet coated therewith", and mainly uses the addition of nano MoS2 and modified nano polytetrafluoroethylene particles in the treatment agent to achieve solid lubrication of the coating. 2 A lubricating coating having an adhesion amount of 0.01% is formed on the surface of the steel sheet by roll coating and baking hardening. The product of the invention is mainly suitable for the stamping requirements of home appliances and micro-motor shell materials, but does not meet the stamping requirements of high-precision components with large deformation in the automobile and machinery fields, and is not suitable for the surface treatment of ordinary cold-rolled sheets.

[0006] Patent Document 7 discloses "Phosphate pretreated electrogalvanized automobile outer panel compatible with coating, and preparation method thereof". In the invention, a Nb-containing ultra-low carbon steel sheet is designed. After a continuous plating layer is formed on the surface of the steel sheet by gravity electroplating, a 1.0-2.0 g / m2 coating layer is applied. 2 The phosphate pretreatment layer is formed by double-sided spraying method at a phosphating temperature of 50-60°C, and then subjected to oil coating treatment to obtain a product that meets the stamping lubrication and corrosion resistance requirements of automobile body materials. Although the obtained product can be well applied in automobile body production lines, it cannot meet the stamping requirements of large deformation of high-precision components in automobile and machinery fields, and cannot realize the manufacturing requirements for differential double-sided lubrication function.

[0007] Patent Document 8 discloses a "phosphating-saponification production process" involving a drum-type continuous phosphating / saponification process for processing small parts. The process mainly includes the following steps: entering the drum → degreasing → first rinse → phosphating → second rinse → surface conditioning → saponification → exiting the drum. Here, the phosphating temperature is 60-85°C, the dip time is 3-10 minutes, the saponification temperature is 55-80°C, and the dip time is 0.5-5 minutes. This process implements the surface lubrication function of the finished parts through the high-temperature phosphating and saponification processes, which is not suitable for the continuous production of steel strips.

[0008] Patent Document 9 discloses "Phosphating-Saponification Process for 27SiMn Steel", which provides a surface lubrication treatment method suitable for high-precision cold drawn steel pipes, including: for 27SiMn steel parts, pickling→high-temperature phosphating (70°C)→saponification. Similarly, this application adopts non-differentiated treatment on both sides, which is not suitable for continuous production of steel strips.

[0009] From the above, it can be seen that shell parts with high precision and large deformation require two surfaces of the material to have different lubrication functions. The conventional process achieves differential lubrication of steel sheets by applying a coating (plastic lubricating coating) or lubricant to the surface in contact with the male mold during stamping. However, this approach does not meet the requirements of high efficiency and environmental protection. Current technology mainly focuses on lubrication devices, lubricant application methods, and precision stamping lubricant compositions for stamping processes. With the increasing demand for shell parts with high precision and large deformation, it will become a requirement of the industry to simplify the processing and production process to produce more cost-effective and competitive products. Therefore, it is necessary to provide a steel strip with excellent performance (e.g., processability and corrosion resistance), high efficiency, and environmental compatibility (e.g., no oil coating), as well as a production method thereof. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 5076347 specification [Patent Document 2] Special Publication No. 8-295985 [Patent Document 3] Korean Patent No. 376927 [Patent Document 4] Chinese Patent No. 104451638 [Patent Document 5] Chinese Patent No. 103289569 [Patent Document 6] Chinese Patent No. 105463436 [Patent Document 7] China Patent Application Publication No. 111349867 [Patent Document 8] China Patent Application Publication No. 105018920 [Patent Document 9] China Patent Publication No. 105296997 Summary of the Invention

[0011] The object of the present invention is to provide a steel strip without oil coating, which has excellent workability and corrosion resistance, and a method for producing the same. The two surfaces of the steel strip have differentiated functions in the thickness direction. The upper surface (i.e., the surface with the phosphate treatment layer and the stearic acid lubricant layer) has a surface roughness R of 0.6 to 1.8 μm. a and surface roughness R of 6 to 16 μm z The lower surface (i.e., the surface having only the stearic acid lubricant layer) has a surface roughness R of 0.3 μm or less, which provides good surface lubrication during the spreading process. a and surface roughness R of 2μm or less zIt has good lubricity and high surface cleanliness. Therefore, the steel strip provided by the present invention can meet the requirements of continuous high-efficiency stamping process for shell parts with high precision and large deformation, and eliminate the need for coating, oiling, and post-forming cleaning during the stamping process of manufacturing shell parts with high precision and large deformation by using traditional steel sheets. The obtained parts can be directly packaged and delivered, so that the efficiency of part manufacturing can be greatly improved. Moreover, the steel strip has good rust and corrosion resistance, and the obtained parts do not need anti-rust oil coating during storage and transportation.

[0012] In one aspect, the present invention provides a steel strip, the steel strip comprising a substrate, and a phosphating layer and a stearic acid lubricant layer disposed on the substrate, the phosphating layer and the stearic acid lubricant layer being disposed on an upper surface of the substrate, in that order, from inside to outside, in a thickness direction of the substrate, and the stearic acid lubricant layer being disposed on a lower surface of the substrate, the upper surface of the steel strip having a surface roughness R of 0.6 to 1.8 μm. a and surface roughness R of 6 to 16 μm z The lower surface of the steel strip has a surface roughness R of 0.3 μm or less. a and surface roughness R of 2μm or less z has.

[0013] Preferably, in addition to Fe and unavoidable impurities, the substrate contains the following chemical elements in wt%: C: 0.1-0.7%, 0.2%≦Si≦2%, 0.2%≦Mn≦2%, Cr: 0.2-1.4%, 0.01%≦Al≦0.06%, and Mo: 0.05-0.2%, where the unavoidable impurities include P≦0.04% and S≦0.05%.

[0014] In order to more clearly describe the present invention, it should be noted that "top" and "bottom" (or "upper side" and "lower side") are used to distinguish two surfaces (or sides) of a substrate or steel strip in the thickness direction. Specifically, in this specification, the surface or side having a phosphating layer and a stearic acid lubricant layer is referred to as the "top" or "upper side", and the surface or side having only a stearic acid lubricant layer is referred to as the "lower" or "lower side". However, such descriptions are not intended to unduly limit the present invention, as those skilled in the art will understand that the terms "top" and "lower" are relative descriptions that change depending on the orientation of the product.

[0015] As used herein, when describing the relative positions of the phosphating layer and the stearic acid lubricant layer on top of a substrate, "inside out" refers to the direction from closer to the substrate to the side farther from the substrate. For example, in Figure 1, "inside out" refers to the direction from bottom to top.

[0016] Preferably, the substrate contains the following chemical elements in wt%: C: 0.1-0.7%, 0.2%≦Si≦2%, 0.2%≦Mn≦2%, Cr: 0.2-1.4%, 0.01%≦Al≦0.06%, Mo: 0.05-0.2%, the balance being Fe and unavoidable impurities, where the unavoidable impurities include P≦0.04%, S≦0.05%.

[0017] In the steel strip substrate according to the present invention, the design principle of the content of each element is as follows:

[0018] C: When the content of element C is less than 0.1%, the strength is insufficient. When the content of element C is more than 0.7%, the chemical reactivity of the surface of the material will be reduced, thereby affecting the phosphating and passivation film formation of the surface. The molding stability of the material may be insufficient. Therefore, the content of element C is controlled to be in the range of 0.1%-0.7%.

[0019] Si: Elemental Si can effectively improve the formability (moldability) of materials in high strength conditions. However, if the content of Si is too high (>2%), it will be selectively oxidized and precipitated during heat treatment, and the precipitate will be concentrated on the surface, thereby affecting the subsequent phosphating and passivation film formation reaction performance. Therefore, the content of elemental Si is controlled to be in the range of 0.2%~2%.

[0020] Mn: element Mn can play a role in ensuring the strength and hardness of the material. However, if the Mn content is too high (>2%), it will also be selectively oxidized and precipitated during the heat treatment process, and the precipitates will be concentrated on the surface, thereby affecting the subsequent phosphating and passivation film formation reaction performance. Therefore, the content of element Mn is controlled to be in the range of 0.2%-2%.

[0021] Cr, Al, and Mo: These elements mainly have the function of refining the crystallinity. If the content is too low, the above effect cannot be fully realized. Excessive addition is not economical for product manufacturing. Therefore, the contents of elements Cr, Al, and Mo are controlled to be in the ranges of 0.2%~1.4%, 0.01%~0.06%, and 0.05%~0.2%, respectively.

[0022] The unavoidable impurities include the elements P and S. If the content of P and S is too high, it will affect the toughness of the material and cannot meet the requirements of formability in large deformation. Therefore, the content of the impurity elements P and S is controlled not to exceed 0.04% and 0.05%, respectively.

[0023] Preferably, the substrate has a thickness of 1.0-6.0 mm. In this specification, the "substrate thickness" does not include the thickness of one phosphate layer and two stearic acid lubricant layers on the upper and lower surfaces of the substrate. If the substrate thickness is less than 1 mm, the shell wall of the part is likely to be too thin to meet the load-bearing performance requirements after large deformation and deep drawing. If the substrate thickness is more than 6 mm, the production line for producing cold rolled products cannot realize effective production. With a substrate thickness of 1.0-6.0 mm, the steel strip according to the present invention is suitable for processing shell parts with high precision and large deformation.

[0024] Preferably, the phosphating layer has a grain size (i.e. the maximum length of the grains) of 8-20 μm, in which the crystal grains are elongated, the grain size being measured according to standard GB / T38933-2020.

[0025] Preferably, the phosphating layer (i.e., the phosphating coating) has a thickness of 1 to 3 g / m 2 and is measured according to standard GB / T38933-2020.

[0026] Grain size of the phosphating layer between 8 and 20 μm and / or between 1 and 3 g / m 2 Due to the weight of the phosphating layer, on the one hand, it can better provide a three-dimensional space for the subsequent stearic acid film formation, thereby effectively increasing the retention capacity of the stearic acid lubricant on the product surface. On the other hand, it can better ensure the uniform distribution of the lubricant during the deformation process and provide additional lubrication by utilizing its good friction lubrication properties. The phosphating layer according to the present invention is a non-dense phosphating film with coarse crystals, which effectively reduces the amount of wear debris during the stamping process, thereby extending the life of the die.

[0027] The top surface of the steel strip according to the present invention comprises a phosphating layer and a stearic acid lubricant layer, in that order from inside to outside. That is, the top surface is designed with a structure of a phosphating layer and a stearic acid coating. Both the phosphating coating and the stearic acid saponification coating have lubricating functions, and their combination can effectively improve the lubrication stability during the stretch deformation process. The top surface has a surface roughness R of 0.6-1.8 μm. a and surface roughness R of 6 to 16 μm z which can ensure that the surface of the steel strip has good surface lubrication during the rolling process.

[0028] The underside of the steel strip according to the present invention is a stearic acid lubricant layer. Stearic acid is a processing lubricant that provides both internal and external lubrication. It has good thermal stability and excellent release performance (prevents sticking and accumulation on the surface of the mold) during the high speed continuous stamping process, and avoids abnormal abrasive particle contamination of the inner surface of the formed parts. It ensures surface lubrication and high surface cleanliness. The underside has a surface roughness R of less than 0.3 μm. a and surface roughness R of 2μm or less z has.

[0029] The upper and lower surfaces of the steel strip according to the present invention have a structure design with differentiated functions, which can provide the individualized functional requirements during the forming and stamping process demanding high efficiency and high precision.

[0030] The surface of the steel strip according to the present invention, which is in contact with the female mold during the forming process, is a phosphate treatment layer and a stearic acid lubricating layer. The surface has good surface lubrication performance during the rolling process. The surface has a surface roughness R a : 0.6~1.8μm and surface roughness R z : The surface roughness of the steel strip surface in contact with the female die is too low, i.e. R a <0.6μm or R z When the surface roughness is too high, i.e., R<6μm, the surface lubricating components will be lost at a high rate during the deformation and spreading process, leading to insufficient lubrication performance and scratches on the material surface, thus damaging the die.a >1.8μm or R z When >16 μm, the lubrication during the deformation and spreading process is sufficient, but excessive wear debris will be generated during successive stamping, thereby affecting the life of the die.

[0031] The surface of the steel strip according to the invention, which is in contact with the male die during the forming process, is a stearic acid lubricant layer. The surface has good lubrication and high surface cleanliness. The surface has a surface roughness R a ≦0.3μm and surface roughness R z ≦2 μm. The surface of the strip in contact with the male die is the inner surface of the formed part. A smoother surface design can meet the high dimensional accuracy requirements of the formed part. At the same time, the surface is in intimate contact with the die during the forming process. A suitable surface lubricating component will provide sufficient lubrication during the forming process. If the surface roughness of the strip surface in contact with the male die is too high, i.e., R a >0.3μm or R z When >2 μm there will be an increased risk of poor dimensional accuracy and smoothness of the inner surface of the molded parts.

[0032] The upper and lower surfaces of the steel strip according to the present invention adopt differentiated functional design, in which the surface of the steel strip in contact with the male mold has good lubrication and high surface cleanliness, and the surface of the steel strip in contact with the female mold has good surface lubrication performance during rolling. According to the present invention, the requirement of continuous and efficient stamping process during processing of shell parts with high precision and large deformation can be met, and steps such as film coating or oil coating during the stamping process of manufacturing shell parts with high precision and large deformation by using traditional steel sheets can be omitted. The obtained product can be packaged and then shipped as it is, eliminating the need for cleaning after forming and significantly improving production efficiency.

[0033] At the same time, both the upper and lower surfaces of the steel strip have stearic acid. After the stearic acid is formed into a coating, it has excellent corrosive medium barrier function at room temperature, which can effectively improve the rust resistance and corrosion resistance of the steel strip surface. The parts produced by the steel strip do not need additional anti-rust oil coating.

[0034] In another aspect, the present invention provides a method for producing a steel strip (e.g., a steel strip as described above), comprising: 1) Degreasing: A step of feeding the rolled steel material into a degreasing tank containing an alkaline degreasing agent by a tension roller and degreasing the steel material at a degreasing temperature of 30 to 60°C, in which oil stains on the surface of the steel material can be cleaned by using the alkaline degreasing agent; 2) First rinse: Rinse the degreased steel surface with rinse water, where the rinse water is industrially pure water having a conductivity of ≦10 μS / cm, or the rinse water is a mixture of tap water with 0.2-1.1 wt% of a corrosion inhibitor; 3) Activation and passivation: spraying a surface conditioner on the upper surface of the rinsed steel with a spray pressure of 0.4-1.2 bar in a spray direction that forms an included angle of 90-135° with the moving direction of the steel to activate it, and coating a passivation treatment agent having phosphating and barrier functions on the lower surface of the steel to passivate it; 4) Phosphating: subjecting the upper surface of the activated steel to a phosphating treatment by high pressure spraying of a phosphating agent, the phosphating treatment being carried out for a time of 6-12 seconds, at a spray pressure of 5-8 bar, with a spray direction forming an included angle of 90-135° with the direction of movement of the steel; 5) Second rinse: Rinse the surface of the steel with industrially pure water having a conductivity of ≦10 μS / cm, and then subject the surface of the steel to a rinsed wring-dry treatment surface; 6) Saponification: applying a stearic acid treatment agent to the upper and lower surfaces of the steel at a temperature of 70-90°C, and then treating the surface of the steel with compressed air purging and wiping rollers.

[0035] Preferably, in step 2), the surface of the steel material is rinsed by a spraying method, and the spray pressure is 2-4 bar.

[0036] Preferably, in step 2), the corrosion inhibitor is selected from one or more of sodium phosphate, sodium nitrite, sodium benzoate, and sodium silicate.

[0037] Preferably, in step 3), the surface conditioner is selected from surface conditioners based on colloidal titanium salts, such as PL-Z available from Parkerizing.

[0038] Preferably, in step 3), the phosphating and passivating agent with barrier function is a zirconic acid-based passivating agent or a chromate-based passivating agent.

[0039] Preferably, in step 4), the phosphating agent is selected from zinc-manganese-nickel ternary phosphating solutions, such as PB-181 available from Parkerizing.

[0040] Preferably, in step 4), the spray angle is 100 to 120° with respect to the moving direction of the steel material.

[0041] Preferably, in step 5), the surface of the steel material is rinsed by a spraying method, the spray pressure is 1-4 bar, and the spray angle is 90-120° with respect to the moving direction of the steel material.

[0042] Preferably, in step 6), the stearing agent is applied by spraying.

[0043] Preferably, in step 6), the stearic acid contained in the stearing agent is C18 or C16 stearic acid.

[0044] Preferably, in step 6), the stearing agent comprises one or more of sodium stearate, magnesium stearate, and zinc stearate.

[0045] Preferably, in step 3) and / or step 4), the movable baffles are provided at a distance of 2-6 cm, preferably 3-5 cm, from both edges of the steel material in the width direction of the steel material, respectively. In other words, the movable baffles are approximately in the same plane as the steel material and perpendicular to the length direction (i.e., the moving direction) of the steel material, and the gap between the movable baffles and the edges of the steel material is 2-6 cm, preferably 3-5 cm.

[0046] Preferably, in step 3) and / or step 4), the steel material moves at a speed of 40 to 80 m / min.

[0047] In the method of the present invention, The main purpose of degreasing is to effectively clean the surface of steel. The temperature of the degreaser is controlled within 30-60℃. If the temperature is too low (<30℃), the cleaning ability will be significantly reduced, making it difficult to guarantee the surface cleanliness, or a large amount of cleaning additives will be required, which is not good for the environment. If the temperature is too high (>60℃), the energy consumption will be too high to meet the low-carbon production requirements.

[0048] The residual degreaser on the surface of the steel material is washed and removed by the first rinse, and the cleaning effect is confirmed by the continuous state of the surface water film. Rust problems can easily occur during the first rinse process. This can be effectively avoided mainly by the quality of the rinse water and corrosion inhibition technology. The corrosion process of metal materials in water is mainly an electrochemical reaction, and the conductivity of the water directly affects the difficulty of the rust reaction. The conductivity of the water is affected by the number of ionic impurities, which is mainly characterized by the conductivity. The newly degreased metal surface is vulnerable to rust. The rinse process uses industrial pure water with a conductivity of ≦10μS / cm, which can effectively control the rust problem.

[0049] Tap water with 0.2-1.1 wt% corrosion inhibitor can effectively reduce the risk of surface rust during the cleaning process while thoroughly cleaning the surface. When the amount of corrosion inhibitor added is too low (i.e., <0.2 wt%), the corrosion inhibition effect cannot be achieved. When the amount is too high (i.e., >1.1 wt%), it is economically and environmentally unfavorable. The added corrosion inhibitor is selected from one or more of sodium phosphate, sodium nitrite, sodium benzoate, and sodium silicate.

[0050] Activation and passivation: On the one hand, a surface conditioner is sprayed on the upper surface of the steel material to form a surface conditioner activation layer that promotes homogeneous nucleation of phosphating. On the other hand, a passivation treatment agent with phosphating and barrier functions is applied to the lower surface of the steel material to form a rust-resistant passivation layer with phosphating and barrier functions. In the process of activation and passivation, it is necessary to effectively control the mutual interference in the treatment process of the upper and lower surfaces. Preferably, during the process of spraying the surface conditioner, the spray pressure is controlled within 0.4-1.2 bar. When the pressure is too low (less than 0.4 bar), the spray amount of the surface conditioner is insufficient, resulting in insufficient activation. When the spray pressure is too high (greater than 1.2 bar), it will also affect the adsorption amount of the surface conditioner, resulting in insufficient treatment of the phosphating of the product. When the spray angle is 90-135°, preferably 100-120°, relative to the moving direction of the steel material, the influence of the surface conditioner on the lower surface can be better avoided.

[0051] The method of applying the phosphate treatment and the passivation treatment agent having a barrier function to the surface of the steel material may be spraying, roller coating, brush coating, etc. When the spraying method is applied, the spray angle with respect to the moving direction of the steel material should be controlled so as to reduce the mutual interference of the treatment agents on the upper and lower surfaces caused by the splashing of the spray.

[0052] It is preferred that the movable baffle is provided at a distance of 2-6 cm from the edge of each side of the steel to avoid interference between the two surfaces during the spraying process. The main purpose is to avoid cross-contamination of surface treatments during the spraying process. If the gap between the steel and the movable baffle is too large (>6 cm), different treatments on the upper and lower surfaces will significantly affect each other during the spraying process. If the gap between the steel and the movable baffle is too small (<2 cm), there is a greater risk that the edges of the steel will hit each other during normal production. The gap between the steel and the movable baffle is preferably 3-5 cm.

[0053] The main purpose of phosphating is to rapidly form uniformly distributed phosphating crystal particles on one side of the steel, so that the coating can be formed quickly, uniformly, and non-densely (see Figure 1). By spraying the phosphating agent at high pressure, the phosphating coating is formed within 6-12 seconds. This is a non-dense phosphating coating, with particle length in the range of 8-20 μm and density of 1-3 g / m. 2 The phosphate coating layer is composed of long plate-like phosphate crystal particles with a phosphate coating weight (i.e., the weight of the phosphate layer) of 10 ...

[0054] The processing time of conventional continuous phosphating of steel is generally more than 15 seconds. In the present invention, the processing of effective surface phosphating can be performed within 6-12 seconds by using high pressure spray and controlling the spray pressure to be within 4-10 bar. Therefore, the phosphating efficiency can be greatly improved. When the spray pressure is too low (<4 bar), the phosphating efficiency of the continuous manufacturing process does not meet the requirements of rapid (6-12 seconds) phosphating processing, and the size of the resulting phosphating crystals is small (particle length <8 μm), which does not meet the surface requirements of the continuously produced steel products. When the spray pressure is too high (>10 bar), excessive splashing occurs, which easily affects the lower surface, and adversely affects the stability of the phosphating effect and the uniform distribution of the phosphating crystals. The spray direction is at an angle of 90-135°, preferably 100-120°, to the moving direction of the steel.

[0055] Second rinsing: The main purpose of this is to effectively clean the phosphating treatment agent remaining on the surface. The risk of rust in this process is significantly reduced due to the effect of the phosphating film and passivation film on the surface of the steel, eliminating the need for special rust prevention control. Both sides of the steel are rinsed with industrial pure water with a conductivity of ≦10 μS / cm. The temperature of the rinsing water is room temperature, and the spray pressure is 1-4 bar. The spray direction forms an angle of 90-120° with the moving direction of the steel. If tap water with high conductivity is used as it is, electrolyte residues will be left on the surface. This will be directly covered with the stearic acid lubricant film in the subsequent process, and therefore affect the rust resistance of the product during storage and transportation. The surface is squeezed dry after rinsing (for example, by using a squeeze roll or a squeezer), and the amount of water on the surface can be effectively reduced.

[0056] Stearic acid treatment (saponification treatment): liquid stearic acid is applied to the surface of the steel material by spraying at 70-90°C, and the surface coating layer is treated to be uniform by using a wiping roller. Preferably, the stearic acid is C18 or C16 stearic acid. Preferably, the stearic acid treatment agent is formulated from one or more of sodium stearate, magnesium stearate, and zinc stearate. After the liquid stearic acid is sprayed on the surface of the steel material, it is blown by compressed air, and the wiping roller ensures the uniform treatment of the surface coating.

[0057] After the above steps are completed, the steel strip is wound by a winder and then packaged for delivery. The steel strip produced by the above described method exhibits excellent rust and corrosion resistance, so that it does not require additional rust-preventive oil coating during storage and transportation.

[0058] The beneficial effects of the present invention are as follows: 1. According to the present invention, a steel strip can be obtained whose two surfaces have differentiated functions, where the surface with only a stearic acid lubricant layer has good lubricity and high surface cleanliness, and the surface with a phosphating layer and a stearic acid lubricant layer has good surface lubricity during the rolling process. This meets the requirements of a continuous and efficient stamping process during the processing of shell parts with high precision and large deformation. However, when using conventional steel sheets, it is necessary to carry out film coating and oil coating during the stamping process to manufacture shell parts with high precision and large deformation, and the parts need to be cleaned after they are processed into parts. Rather, when using steel strips according to the present invention, shell parts with high precision and large deformation can be directly stamped and processed. Compared with conventional steel sheets, the steps of film coating, oil coating, or cleaning after forming can be omitted, and the obtained parts can be directly packaged and delivered. As a result, the efficiency of part manufacturing can be greatly improved. Moreover, stearic acid is applied to both sides of the steel strip. After forming the stearic acid into a coating, the rust resistance and corrosion resistance of the surface of the steel strip can be effectively improved, and the steel strip does not need to be coated with anti-rust oil during storage and transportation. 2. In the manufacturing method provided by the present invention, after the substrate is degreased and rinsed, the two surfaces of the substrate are activated and passivated respectively, and the process parameters are controlled to prevent interference between the treatment of the two surfaces, and a one-sided phosphating spray process combined with a two-sided saponification process is used to realize the continuous production of steel strip with differentiated functions on two surfaces. 3. The high pressure spray phosphating process of the present invention significantly reduces the effective treatment time under suitable machine length conditions. The overall feed rate of the steel strip can be controlled within 40-80m / min, and the requirements of highly efficient production of conventional steel strip can be met, so that the method can be directly connected to the existing continuous annealing and leveling process of cold rolled steel strip, and can also be used as an independent surface treatment mode to realize the continuous production of steel strip with differentiated functions of the two surfaces. [Brief description of the drawings]

[0059] [Figure 1] FIG. 1 is a schematic structural diagram of a steel strip according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] The present invention will be described in detail below with reference to the figures, examples, and comparative examples. However, the present invention is not limited to the following examples.

[0061] 1, which shows the structure of a steel strip provided by an embodiment of the present invention. Surface A of the substrate includes, from inside to outside, a phosphating layer 1 and a stearic acid lubricant layer 2, and surface B of the substrate is a stearic acid lubricant layer 2. EXAMPLES

[0062] Table 1 was referenced for the substrate compositions of the examples and comparative examples of the present invention. The balance is Fe and unavoidable impurities other than P and S. Table 2 shows the manufacturing process parameters of the examples and comparative examples of the present invention. Table 3 shows the evaluation results of the implementation effects of the processes in the examples and comparative examples of the present invention.

[0063] Two surface roughness parameters Ra ("arithmetic mean deviation") and Rz ("ten-point average of microirregularities") of the steel strip are measured by using a Mahr MARSURF-PS10 portable roughness tester from Marl, Germany (measurements are made with reference to standard GB / T1031).

[0064] The effectiveness of the implementation of the process according to the present invention was evaluated according to the following evaluation criteria.

[0065] (1) Process--Evaluation of degreasing effect The degreasing and cleaning effect on the surface of the steel strip was evaluated by the continuous state of the water film on the surface during the water washing process after degreasing. The state of the water film on the washed surface after degreasing was visually observed: ⊚: The water film on the surface is uniform and continuous, with a coverage rate of 100%. ×: The water film on the surface was clearly discontinuous, and had a coverage rate of less than 100%.

[0066] (2) Process--Rust phenomenon after rinsing 1 The condition of the rust on the surface of the steel strip before activation and passivation and after the first rinse was visually observed: ⊚: The surface had no rust, and the rust / area was 0%. ×: There were rust spots on the surface, and the rusted area was greater than 0%.

[0067] (3) Process--phosphating effect After phosphating, samples were taken. The size of the phosphating crystals on the top surface of the phosphating steel strip was observed by SEM: ◎: The size of the phosphate crystals on the top surface was 8-20μm, and the crystals were uniformly distributed. 2 Weight of phosphate coating: ≦3g / m 2 . ○: The size of the phosphate crystals on the top surface was 8-20 μm. However, the crystals were distributed unevenly in some areas. 2 Weight of phosphate coating: ≦3g / m 2 . △: The size of the phosphate crystals on the top surface is <8μm or >20μm, and the weight of the phosphate coating is <1g / m 2 or >3 g / m 2 It was. ×: No significant phosphate crystals on the top surface.

[0068] (4) Process--Purification effect Samples were taken after phosphating. The underside of the untreated steel strip after phosphating was observed by SEM: ⊚: No phosphate crystals were observed. ○: Minor phosphorylation was observed in localized areas, but no significant phosphate crystals were observed. △: Slight phosphate crystals were observed on the surface. ×: Significant phosphate crystals were observed on the surface.

[0069] As shown in Table 3, Examples 1 to 6 were processed according to the process described in the present invention, and all the process effects of the obtained steel strips were excellent. The lower surface of the steel strip was a stearic acid lubricant layer, and the surface roughness R was less than 0.3 μm. a and surface roughness R of 2μm or less z Therefore, the lower surface had good lubricity and high surface cleanliness. The upper surface of the steel strip included a phosphate treatment layer and a stearic acid lubricant layer, in that order, from the inside to the outside, and the upper surface thereof had a surface roughness R in the range of 0.6 to 1.8 μm. a and surface roughness R in the range of 6 to 16 μm z and therefore the top surface had good surface lubricity during the spreading process.

[0070] In Comparative Example 1, the lack of phosphating and barrier treatment resulted in significant phosphating crystals forming on the lower surface due to partial phosphating effect. In Comparative Example 2, the degreasing temperature close to room temperature was not able to achieve effective surface cleaning, and the short phosphating time combined with the low spray pressure did not result in significant phosphating crystals on the upper surface. In Comparative Example 3, the use of high conductivity tap water as rinse water 1 caused obvious rust during the water washing process after degreasing, which adversely affected the subsequent phosphating.

[0071] For the steel strip obtained in the examples of the present invention, the surface of the steel strip was subjected to a neutral salt spray test according to the standard ASTM-B117. No rust was observed on the surface of the steel strip after 24 hours. The corrosion resistance of the steel strip was obviously better than that of the conventional oil-coated steel sheet, which showed rust after about 12 hours in the neutral salt spray test. This shows that the steel strip obtained according to the present invention has good rust and corrosion resistance and meets the corrosion resistance requirements of storage and transportation for 4 months without surface rust.

[0072] [Table 1]

[0073] [Table 2]

[0074] [Table 3] [Explanation of symbols]

[0075] 1 Phosphating layer 2. Stearic acid lubricant layer

Claims

1. A steel strip comprising a substrate and a phosphate treatment layer and a stearic acid lubricant layer disposed on the substrate; In the thickness direction of the substrate, the phosphate treatment layer and the stearic acid lubricant layer are disposed in that order from inside to outside on an upper surface of the substrate that contacts a male mold during a molding process, and the stearic acid lubricant layer is disposed on a lower surface of the substrate that contacts a female mold during a molding process; The upper surface of the steel strip has a surface roughness R of 0.6 to 1.8 μm. ａ and a surface roughness R of 6 to 16 μm ｚ and The lower surface of the steel strip has a surface roughness R of 0.3 μm or less. ａ and a surface roughness R of 2 μm or less ｚ having Steel strip.

2. 2. The steel strip of claim 1, wherein in addition to Fe and unavoidable impurities, the substrate further contains the following chemical elements in wt. %: C: 0.1-0.7%, 0.2%≦Si≦2%, 0.2%≦Mn≦2%, Cr: 0.2-1.4%, 0.01%≦Al≦0.06%, and Mo: 0.05-0.2%, wherein the unavoidable impurities include P≦0.04% and S≦0.05%.

3. 2. The steel strip according to claim 1, wherein the substrate contains the following chemical elements in wt. %: C: 0.1-0.7%, 0.2%≦Si≦2%, 0.2%≦Mn≦2%, Cr: 0.2-1.4%, 0.01%≦Al≦0.06%, Mo: 0.05-0.2%, and the balance being Fe and unavoidable impurities, wherein the unavoidable impurities include P≦0.04% and S≦0.05%.

4. The substrate has a thickness of 1.0 to 6.0 mm and a grain size of 8 to 20 μm in the phosphating layer, and / or the phosphating layer has a weight of 1 to 3 g / m ２ 2. The steel strip of claim 1 having a weight of

5. 2. A method for producing a steel strip according to claim 1, comprising the steps of: 1) Degreasing: a step of feeding the rolled steel material into a degreasing tank containing an alkaline degreasing agent by a tension roller and degreasing the steel material at a degreasing temperature of 30 to 60°C; 2) First rinse: rinsing the degreased steel surface with a rinse water that is industrially pure water having a conductivity of ≦10 μS / cm or a mixture of tap water with 0.2-1.1 wt % of a corrosion inhibitor; 3) Activation and passivation: spraying a surface conditioner onto the upper surface of the rinsed steel material at a spray pressure of 0.4-1.2 bar in a spray direction that forms an included angle of 90-135° with the moving direction of the steel material to activate it, and coating a passivation treatment agent with phosphate barrier function onto the lower surface of the steel material to passivate it; 4) Phosphate treatment: subjecting the upper surface of the activated steel to a phosphating treatment by high pressure spraying of a phosphating agent, wherein the phosphating treatment is carried out for a time of 6 to 12 seconds, at a spray pressure of 5 to 8 bar, with the spray direction forming an included angle of 90 to 135° with the direction of movement of the steel; 5) Second rinse: Rinse the surface of the steel with industrially pure water having a conductivity of ≦10 μS / cm, and then subject the surface of the steel to a wringing and drying process after the rinsing; 6) Saponification: applying a stearic acid treatment agent to the upper and lower surfaces of the steel at a temperature of 70-90°C, and then treating the surface of the steel with compressed air purging and wiping rollers.

6. 6. The method according to claim 5, wherein in step 2), the surface of the steel is rinsed by spraying at a spray pressure of 2-4 bar.

7. 6. The method of claim 5, wherein in step 2), the corrosion inhibitor is selected from one or more of sodium phosphate, sodium nitrite, sodium benzoate, and sodium silicate.

8. 6. The method of claim 5, wherein in step 3), the passivation treatment is a zirconic acid-based passivation treatment or a chromic acid-based passivation treatment, and / or the passivation treatment is applied by one or more of spraying, roller coating, and brush coating.

9. 6. The method according to claim 5, wherein in step 5), the surface of the steel is rinsed by spraying at a spray angle of 90 to 120° with respect to the direction of movement of the steel and at a spray pressure of 1 to 4 bar.

10. 6. The method of claim 5, wherein in step 6) the stearating agent is applied by spraying.

11. 6. The method of claim 5, wherein in step 6), the stearic acid contained in the stearate treating agent is C18 or C16 stearic acid, and / or the stearate treating agent includes one or more of sodium stearate, magnesium stearate, and zinc stearate.

12. The method according to claim 5, wherein in step 3) and / or step 4), the movable baffles are provided at a distance of 2 to 6 cm from the edges of both sides of the steel material in the width direction of the steel material.

13. The method according to claim 5, wherein in step 3) and / or step 4), the steel material moves at a speed of 40 to 80 m / min.

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